K and R C, Solution to Exercise 6-6:
K and R C Programs Exercises provides the solution to all the exercises in the C Programming Language (2nd Edition). You can learn and solve K&R C Programs Exercise.
C Program to implement a simple version of the #define processor(i.e , no arguments) suitable for use with C programs, based on the routines of this section, You may also find getch and ungetch helpful.Read more about C Programming Language .

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#include<stdio.h>
#include<ctype.h>
#include<string.h>

#define MAXWORD 100

struct nlist{
 struct nlist *next;
 char *name;
 char *defn;
};
void error(int, char*);
int getch(void);
void getdef(void);
int getword(char *,int);
struct nlist *install(char *,char *);
struct nlist *lookup(char *);
void skipblanks(void);
void undef(char *);
void ungetch(int);
void ungets(char *);


//simple version of #define processor
main()
{
 char w[MAXWORD];
 struct nlist *p;
 while(getword(w, MAXWORD) != EOF)
  if(strcmp(w, "#") == 0)
   getdef();
  else if(!isalpha(w[0]))
   printf("%s",w);
  else if ((p == lookup(w)) == NULL)
   printf("%s",w);
  else
   ungets(p->defn);
}

//getdef:get defination and install it
void getdef()
{
 int c,i;
 char def[MAXWORD], dir[MAXWORD], name[MAXWORD];
 skipblanks();
 if(!isalpha(getword(dir,MAXWORD)))
  error(dir[0],"getdef:expecting a directve after #");
 else if(strcmp(dir,"define") == 0) {
  skipblanks();
  if(!isalpha(getword(name, MAXWORD)))
   error(name[0],"getdef:non alpha name expected"):
   else{
    skipblanks();
    for(i = 0;i <  MAXWORD-1; i++)
     if((def[i] = getch()) == EOF || def[i] == 'n')
      break;
    def[i] = '